RAID Information - Linux RAID-5 Algorithms

This
page provides information on the layout of the segments in the various
RAID-5 structures in Linux.

Linux RAID-5 Algorithms

Software RAID-5 under the LINUX operating system can use one of four algorithms
for the placement of segments among the disks in the array. These will be individually
shown below:

Left Asynchronous

In this layout, the segments are numbered sequentially, starting with the
first non-parity drive in the stripe. The parity drive starts at the left-most
drive, and moves right one drive per stripe. This is the 'standard' RAID-5
layout. It is not the default for Linux.

Left Synchronous

In this layout, the segments are numbered sequentially, starting with the
first drive in the stripe after the parity. The segments wrap. The parity
drive starts at the left-most drive, and moves right one drive per stripe.
This is the default RAID-5 segment layout under Linux.

For large reads, this segment layout is the fastest. This is because each
consecutive group of segments that is no larger than the total number of
disks in the array, will use all the disks in the array.

Right Asynchronous

In this layout, the segments are numbered sequentially, starting with the
first non-parity drive in the stripe. The parity drive starts at the right-most
drive, and moves left one drive per stripe.

Right Synchronous

In this layout, the segments are numbered sequentially, starting with the
first drive in the stripe after the parity. The segments wrap. The parity
drive starts at the right-most drive, and moves left one drive per stripe.